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United States Patent | 5,311,524 |
Carlson ,   et al. | May 10, 1994 |
A fault tolerant three port communications module has two control ports for receiving commands from two computers, and a communications port for transferring data over a communications channel in response to the commands. Each control port includes a select line which carries a select signal with true and false states, mode lines which carry codes that represent the commands, and a write line which carries a respective pulse in sync with each of the codes. The select line, mode lines, and write line of each control port are coupled in the module to a respective inter-processor command decoder having a lead stage and a trail stage. The lead stage detects when a predetermined code occurs on the mode lines and the select signal is false during a first one of the pulses; and, the trail stage generates an output signal that indicates the receipt of an inter-processor command for the module if, during a second pulse that immediately follows the first pulse, the compliment of the predetermined code occurs on the mode lines and the select line is true.
Inventors: | Carlson; Lewis R. (Salt Lake City, UT); Carver, II; John J. (Salt Lake City, UT) |
Assignee: | Unisys Corporation (Blue Bell, PA) |
Appl. No.: | 936812 |
Filed: | August 27, 1992 |
Current U.S. Class: | 714/823 |
Intern'l Class: | H04L 001/08 |
Field of Search: | 371/70,60,61,55,57.1 ;919 364/246.8,244.8,249.1,265,221,222.2,230,230.3,229,229.4,259.6,260,261.1,284.4 |
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4308579 | Dec., 1981 | Dlugos | 371/70. |
4434499 | Feb., 1984 | Motsch et al. | 371/70. |
4866609 | Sep., 1989 | Calta et al. | 395/250. |